Dynamic analysis of planar mechanical systems considering stick-slip and Stribeck effect in revolute clearance joints

Abstract

The phenomena of friction in clearance joints have time- dependent nonlinear characteristics, which could lead to undesirable and unstable dynamic behavior of mechanical systems. Various mathematical models have been proposed to describe friction force in clearance joints. However, most of the previous models have different limitations, such as discontinuity at zero velocity or disability of detecting stick-slip motion. In this paper, a hybrid friction model is presented to analyze the dynamics of planar mechanical systems, considering sliding, sticking and Stribeck effect in revolute clearance joints. According to the kinematic analysis, the relative tangential motion between the journal and the bearing is categorized as sticking state, sliding state and transitional state. In the sticking state, an assumed acceleration constraint for the contact points is proposed to estimate the static friction force. This method not only eliminates the calculation of the implicit external force, but also accurately reflects the sticking process in accordance with the friction physics. Furthermore, the Stribeck effect is introduced in the description of the friction force in the sliding state, revealing the influence of the sliding velocity on the friction force. The stick-slip motion could also be accurately described by the Stribeck effect, which guarantees the continuity of the friction force during the transition process. Finally, a space robot manipulator is taken as an example to demonstrate the hybrid friction model. Dynamics of the space robot manipulator with Coulomb friction model, LuGre friction model, Wojewoda friction model and the hybrid friction model are compared, respectively. And the effects of clearance size, static friction coefficient and sliding friction coefficient on the dynamics of the manipulator are also analyzed.